Field of the Disclosure
Embodiments disclosed herein relate generally to continuously variable transmissions, and more particularly to methods, assemblies, and components for continuously variable transmissions (CVTs).
Description of the Related Art
Continuously variable transmissions are becoming more popular as people understand the benefits and advantages of having a continuous range of transmission ratios instead of a finite set. There are well-known ways to achieve continuously variable ratios of input speed to output speed. Typically, a mechanism for adjusting the speed ratio of an output speed to an input speed in a CVT is known as a variator and a control system manages the variator so that the desired speed ratio can be achieved in operation. In a belt-type CVT, the variator consists of two adjustable pulleys coupled by a belt. A disadvantage to belt-type CVTs is the necessity of two axles—a drive axle and a driven axle—that are offset from one another and are not coaxial. In a single cavity toroidal-type CVT, the variator usually has two partially toroidal transmission discs rotating about a shaft and two or more disc-shaped power rollers rotating on respective axes that are perpendicular to the shaft and clamped between the input and output transmission discs. A common issue with toroidal-type CVTs is the variation in forces requires a robust and dynamic axial force generation system. In addition to adding cost and complexity to the system, these axial force generation systems add additional parasitic losses to the CVT.
Embodiments of the variator disclosed herein are of the ball type variator utilizing planets (also known as power or speed adjusters, balls, sphere gears, or rollers) that each has an axle defining a tiltable axis of rotation adapted to be adjusted to achieve a desired ratio of output speed to input speed during operation. The planets are angularly distributed about a longitudinal axis in a plane perpendicular to the longitudinal axis of a CVT. The planets receive power on one side from an input disc and transmit power on the other side to an output disc, one or both of which apply a clamping contact force for increased transmission of power. The input disc applies (input) power at an input torque and an input rotational speed to the planets. As the planets rotate about their own axes, the planets transmit the (output) power at an output torque and an output rotational speed to the output disc. The output speed to input speed ratio is a function of the radii of the contact points of the input and output discs to the axes of the planets. Tilting the axes of the planets with respect to the axis of the variator adjusts the speed ratio. The planets may receive or transmit power via direct contact with the input or output disc, or via contact with any of a type of fluid capable of transmitting power.
There is an ongoing desire for variators and control systems that provide improved performance and operational control.